1. Field of the Invention
This invention relates to solar heat collectors. More particularly, it relates to a solar heat collector the shape of which provides increased heat collecting volume as compared to flat collecting panels of the same base area and enables the collector to provide heated fluid in a fixed position--i.e. without the necessity for tracking the sun--and on both cloudy and clear days.
2. Description of the Prior Art
As solar heat collectors have increased in numbers and popularity, the number of designs has also increased. The most common design for small scale use--e.g., domestic hot water heating and the like--has been a panel design, in which the collector module is a rectangular panel having a flat surface facing the sunlight. The flat surface is generally light transmissive and serves as a cover for one of numerous possible arrangements for moving air or fluid through the collector to be heated. See for example, U.S. Pat. Nos. 4,067,319; 4,120,282; and 4,136,669. Generally, panel collectors or elements thereof should "track" the sun for optimum operation, although many installations are permanently fixed at an angle which provides maximum heating at the latitude of use during clear winter days when heat is most needed. Panel collectors are in wide use and function satisfactorily, but they have the disadvantages that they are often complex and expensive to construct and frequently three or four or more panels are required to obtain the desired amount of heating.
In another approach to solar collector design, Thannhauser U.S. Pat. No. 3,254,644 discloses an upwardly concave conical thermosyphon in which a light-absorbing metal tube or non-metallic hose lines the inner surface of an upwardly open cone mounted with its axis perpendicular to the earth's surface. This unit presents at least a portion of the heat absorbing surface perpendicular to the sun's rays during the daylight hours. Fluid to be heated, e.g. water, enters the Thannhauser unit at the bottom of the cone--i.e. at its apex--and as it is heated thermosyphon action causes it to move through the tube in a spiral path toward the top of the unit where the outlet is located.
Thannhauser's thermosyphon is simple in design but because it is a thermosyphon the rate of fluid circulation through it is slow; moreover, if pump means were used to circulate the fluid at a higher rate, the single conical shape would have to be impractically high to provide sufficient heating surface for any significant heating. Another disadvantage of the Thannhauser unit is that its upwardly open conical shape not only results in little if any heating on overcast days but also acts as a cup to catch falling leaves, etc., thereby causing upkeep and cleaning problems.